Production of sodium perchlorate



rates 3,038,782 Patented .lune l2, 1962 My invention relates to a process for the production of sodium perchlorate by the oxidation of sodium chlorate using lead dioxide in a reaction medium containing sulfuric acid. y

It is known to convert chlorates to perchlorates using lead dioxide and sulfuric acid. Whenthe chlorate chosen is sodium chlorate, the reaction is as follows: i

This is shown, for example, in application Serial No. 331,- 738, filed January 16, 1953, by Daniel I. Jaszka and me, now U.S. Patent 2,853,362. Thus, that application describes the reaction of alkali metal and alkaline earth metal chlorates, preferably the stoichiometric amount of lead dioxide and preferably about 1.5 or 2 to about 6 moles of sulfuric acid per mole of lead dioxide, to form the corresponding alkali metal or alkaline earth metal perchlorate at reaction temperatures preferably of about 90 to about 120 C.

When this process is utilized for converting sodium chlo rate to sodium perchlorateJ it is found that difficulty is en countered in separating the sodium perchlorate produced from the reaction mixture. Specifically, upon completion of the oxidation reaction it is found that, due `to its high viscosity, the reaction mixture is difiicult to lter to provide a filtrate containing sodium perchlorate dissolved therein, and also that, because of the sigh solubility of the sodium perchlorate in the filtrate, it is difficult to separate the sodium perchlorate therefrom in solid form.

In accordance with my present invention, I have discovered that these difficulties can vbe conveniently overcome by including in the reaction mixture as an initial ingredient at least a molar amount of perchloric acid, based upon the moles of sodium chlorate present. When this is done, the reaction mixture at the end of the reaction period has a viscosity such that it can be conveniently filtered to provide a filtrate in which lthe sodium perchlorate is relatively insoluble, so that it can be conveniently separated therefrom as a solid. The oxidation can be carried out in about one hour with low cost equipment to produce sodium perchlorate in yields as high as about 98 percent, based upon sodium chlorate and on lead dioxide. The sodium perchlorate produced is free from undesirable impurities, such as lead, chlorate, chloride and sulfate ions.

The following examples illustrate in detail the practice of my invention.

EXAMPLE l A mixture consisting of 34.1 grams H2S04 (96%), 149.8 grams HClO'.,t (60%), 65.2 grams H20, 71.8 grams Pb02 and 32.0 grams NaCl03 is reacted in a three neck flask with constant agitation for two hours at 100 C. A CaO2 trap is employed in the system to collect any gases formed. The reaction mixture is immediately filtered hot and the residue washed to remove adhering NaCl04, HC104 and H2804. The filtrate and washing are combined and analyzed for C103- ions and C104- ions. The solution from the trap is also analyzed to determine whether any NaCl03 was lost as Cl02. The analysis shows that a ield of NaCl04 is obtained with only an 0.8% loss of NaCiO3 as C102. tion and cooling of the combined filtrate and washing results in lthe precipitation of sodium perchlorate crystals.

EXAMPLE l-I A mixture consisting of 68.2 grams H2804 (96%), 300 grams H0104 (60%), 130.4 grams H20, 143.6 grams Pb02 and 64.0 `grams NaCl03 is reacted at 98 C. in a three neck flask with constant agitation. A CaO2 trap is employed to collect any gases formed. To check the rate of reaction small samples are removed at definite time intervals throughout the'run. Analysis shows that after 2.33 hours an 82% yield of NaCl04 is obtained with only a 0.1% loss of NaCl03 as C102. The reaction mixture is filtered hot. Evaporation and cooling of the filtrate results in the production of sodium perchlorate crystals.

EXAMPLE III A mixture consisting of 58.8 grams H2804, 151.() grams HC104, 132.4 grams H20, 143.5 grams P1302, 20.8 grams NaClO., and 54.0 grams NaCl0'3 is reacted in a three neck iiask with constant agitation for SA hour at 98-l00 C. A CaO2 trap is employed to collect any gases formed. The reaction mixture is filtered and the residue washed with H20 to remove adhering NaCl04, HC104 and H2804. The ltrate and washings are analyzed for C103` ion and C104 ion indicating a 100% yield of NaCl04. Analysis of the trap solution showed that no NaClO3 is lost as Cl02. Evaporation and cooling,7 of the combined filtrate and Washing results in the precipitation of sodium perchlorate crystals.

EXAMPLE IV In order to test my process further, a series of seven cycles was run, in five of which the process liquor was recycled. Stoichiomteric quantities of 13h02, H250.,z and NaClOg were used in the first five cycles, resulting in incomplete conversion of the NaCl03. In cycles six and seven, a 20% excess of 19h02 and H280; was added. Complete conversion of NaCl03 was obtained in these two runs. The cyclic operation of the process was carried out as follows.

A charge consisting, of 0.5 gram -mole 601% H2804 and 1.5 gram moles 60% HCIO., was placed into a 1 liter resin kettle, fitted with a stirrer (Teflon blade), reflux condenser, and thermometer well. While the mixed acids were still cold, 0.5 gram mole NaCl03 and 0.5 gram mole Pb02 were added. The reactor was set in an oil thermostat at room temperature. Heat was applied, and the temperature of the bath was gradually increased to C.; at the end of 2.5 hours heating time, the reactor was removed from the bath, and the contents transferred to a heated medium porosity, sintered glass funnel, and filtered by vacuum to separate the lead salts from the mother liquor. The lead residue was pressed down with a fiat stirring rod. When no more liquor could be removed, the lead residue was slurried with three, fifty ml. portions of hot water, while still on the filter. The washings were added to the original filtrate and the total volume was measured. A small sample (2 ml.) was removed for C103- analysis, and the rest of the liquor was Evaporai placed on a hot plate to evaporate. Heating at this point was continued until the solution attained a temperature of 14C-150 C., after which the solution was allowed to cool.A NaClO4 crystallized upon cooling, starting at a solution temperature of 130 C. The crystals were removed yby lfiltration when the solution temperature reached 25 C. They were pressed down while on the iilter, to remove excess liquor.

Samples of both liquor and crystals were made up to volume for analysis. The remainder of the liquor was recycled in all cases except after cycle six. A fresh solution -was prepared for cycle seven. Its composition was accurately known, and was approximately the same as that obtained from cycle six. This was done for the purpose of obtaining an accurate material balance. In the last two cycles, the filtrate and wash solutions were stored, and analyzed separately. No evaporation was undertaken, and no crystalline product was isolated. Cycles six and seven showed that a excess (above stoichiometric of Pb02 and H2804 aids in complete conversions of the NaClO3, and that the excess of PbOZ is recoverable. NaClO4 crystallized, when the filtrate (after separation of lead salts) was cooled, but -a considerable amount of NaClO4, as well as HClO4 remained in the lead residue, as was shown by the analysis of the wash liquor obtained in cycles six and seven. Data from the seven cycles are listed in Table I.

A typical flow sheet and a complete material 4balance are shown in the accompanying drawing wherein the numerical quantities are in moles. The net equation, as may be calculated from the data presented in the drawing is:

For further details concerning the conversion of lead sulfate to lead dioxide, reference is made to application Serial No. 331,738 mentioned above.

Various modifications can be made in the specific procedures described to provide other embodiments which fall within the scope of my invention, which constitutes an improvement over the heretofore known lead dioxidesulfuric acid method for converting sodium chlorate to sodium perchlorate. Considerable variation can be made in the amount of lead dioxide and sulfuric acid (100% basis) employed. Preferably I operate in such manner that the amount of lead dioxide taken is at least that which is approximately sufficient to oxidize the sodium chlorate to sodium perchlorate complete and the amount of sulfuric acid (100% basis) employed is at least sufijcient to react with all of the lead in the lead dioxide converted, thus converting such lead to lead sulfate. In general lead dioxide is used in the amount of 0.8 to 1.5 moles and sulfuric acid (100% basis) is used in the yamount from 0.8 to 2.0 moles, both ranges being based upon one mole of sodium chlorate originally present in the reaction mixture. Considerable variation can also be made in the amount of perchloric acid (100% basis) initially present in the reaction mixture, but in general the amount of perchloric acid (100% basis) which I use is within the range from 2 to 5 moles, based upon one mole of sodium chlorate. In general, the amount of water initially present in the reaction mixture will be within the range of 57 to 77% of the combined yweight of the aicds. The reaction temperature which I use does not differ critically from those employed in the process heretofore known, although I prefer to operate in the approximate range 90 to 120 C.

Studies have been made involving the direct substitution of perchloric acid for sulfuric acid in the reaction of lead dioxide with sodium chlorate to produce sodium perchlorate. It was necessary, after reaction, to add sulfuric acid, thus precipitating lead sulfate which was removed by liltration. The equations are:

After removal of the lead sulfate, a solution of sodium perchlorate in perchloric acid remained. In one experiment, 0.3 mole of sodium chlorate, 0.3 mole of lead dioxide and percent by weight aqueous perchloric acid containing 1.2 moles of perchloric acid (l00% basis) were reacted at 100 C. for four hours. Upon analysis of the reaction mixture, 1.23 moles of perchlorate were found. This experiment showed that the sodium chlorate was not entirely oxidized to sodium perchlorate, but instead reacted partially with perchloric acid according to the equation:

In effect, perchloric acid was lost as chlorine dioxide and Watl'.

In order to avoid side reactions, the oxidation of sodium chlorate by lead dioxide was accelerated by adding sulfuric acid directly to the initial reaction mixture. By this means, any lead perchlorate formed was precipitated immediately as lead sulfate and virtually no chlorine dioxide was evolved. The equation for this reaction was:

In this experiment, 0.3 mole of sodium chlorate, 0.3 mole of lead dioxide, 0.9 mole of perchloric acid 100% basis) and 0.3 mole of sulfuric acid (100% basis) 4were reacted at 100 CA for two hours. Only 0.8 percent of the sodium chlorate was lost and the conversion of sodium chlorate to sodium perchlorate was percent.

My invention is also applicable to the conversion of potassium chlorate to potassium perchlorate by using an equivalent amount of potassium chlorate for the sodium chlorate in the process heretofore described.

T able l SUMMARY OF SEVEN CYCLES OF LEAD DIOXIDE PROCESS FOR SODIUM PERCHLORATE Cycle I Cycle II Cycle III First Residue First Residue First Residue Crystals Wash-lwash Crystals Wash-lwash Crystals Wash-lwash liquor liquor liquor Charge (moles):

N aClO NaClO 0.13 H0104 1. 50 Has 04. O. 5() Pb02 Products (mo aCl 0.03 NaClOi 0.20 H0104.. 1.35 2S 0. 00

H O4 Residue (moles):

PDO,

not anal.

Tabla` I-Continued Cycle IV Cycle V Cycle VI Cycle VII First; Resi- First Resi- Resi- Resi- Crystals Wash+ due Crystals Wash+ due Liquor Wash due Liquor Wash due liquor Wash liquor Wash Wash Charge (moles):

NaClOa 0.50 0.50 NaClO 0.21 0.12 H0104 1.51 1.49 HzSOl 0.50 0.50 Pb On 0. 50 0. 50 Products (moles):

NaClOa 0.00 0.00 0. 0() 0. 00 0.02 0. 41 0. 06 0 02 0. 50 0. 18 0.06 1.33 0.05 0.05 1.42 HzSO.; 0. 00 0. 00 0. 00 0. 00 0. 00 Residue (moles):

I claim: 20 ture comprising essentially one mole of sodium chlorate,

l. In the oxidation of sodium chlorate with lead dioxide in an aqueous sulfuric acid reaction mixture, the step of including in `such mixture as an initial reactant at least a molar `amount of perchloric acid, based upon the moles of sodium chlorate present.

2. A process which comprises reacting an aqueous mix- 0.8 to 1.5 moles of lead dioxide, 0.8 to 2 moles of sulfuric acid and 2 to 5 moles of perchloric acid to form sodium perchlorate, the amount of water in said mixture being within the range of 57 to 77% of the combined weight of said acids.

No references cited. 

1. IN THE OXIDATION OF SODIUM CHLORATE WITH LEAD DIOXIDE IN AN AQUEOUS SULFURIC ACID REACTION MIXTURE, THE STEP OF INCLUDING IN SUCH MIXTURE AS AN INTIAL REACTANT AT LEAST A MOLAR AMOUNT OF PERCHLORIC ACID, BASED UPON THE MOLES OF SODIUM CHLORATE PRESENT. 